Tunnel an ssh connection through an intermediate machine in a single command

Question

Is there a way, in a single command, to establish a ssh connection from my computer A, through computer B, to computer C, such that I have access to the shell on computer C?

A wrinkle (which seems to rule out simply forwarding the ssh connection using the -L option) is that I have the password to the account on computer B, and the account on computer B is authorized to connect to the account on computer C, but I do not have the password to the account on computer C.

Answer 1

I understood that you want just to log in to the computer C, not really tunnel anything from A to C. So, this should do the trick:

ssh -t computer-b "ssh computer-c"

You might have to enter passwords twice, first for computer B and then for computer C, but this can be avoided by using ssh's key-pair authentication.

Answer 2

You probably want to use SSH's ProxyCommand: http://benno.id.au/blog/2006/06/08/ssh%5Fproxy%5Fcommand

Answer 3

If you're using ssh keys, you could generate a new key for machine B and use that to connection from A to B. On machine B, you can add

command="ssh C" ssh-....

in the ~/.ssh/authorized_keys file. That means that whenever you connect to B with that ssh key, it will execute the ssh C command.

I don't know if this works with scp.